This invention relates to improved well logging methods and apparatus, and more particularly relates to novel methods and apparatus for reducing damage to downhole electronic instrument assemblies caused by vibration and physical abuse.
It is well known that oil and gas are found in subsurface earth formations, and that wells are drilled into these formations to recover such substances. However, it is usually necessary to survey or log the length of the borehole to ascertain if any of the formations contain significant recoverable amounts of oil and gas to justify completing the well.
There is no single well logging technique or device which can provide a direct indication and evaluation of oil or gas in a particular formation of interest. Instead a variety of logging techniques have been devised, which measure various different physical parameters of the earth substances adjacent the borehole. Since no one earth parameter can of itself provide a definitive and conclusive indication of the presence of oil and gas in commercial quantities, there has been a continuing need to perform as many different types of logging measurements as possible.
The various subsurface measuring systems require a considerable amount of downhole electronics circuitry for obtaining the desired subsurface parameter. The severe space restrictions and the rigorous borehole environmental conditions require that the downhole electronics circuitry be sealingly enclosed within a tubular housing of small diameter. To comply with assembly, repair and maintenance requirements of the downhole electronics, typically the electronics circuit components are mounted along a length of narrow metal chassis member which is removably installed within an elongated tubular housing. The enclosure is sealed so as to protect the electronics assembly from exposure to pressure and fluids within the borehole.
In performing typical logging operation, an instrument is lowered, by means of a cable suspending the instrument within the well, to a point in the borehole. The instrument is then caused to traverse the borehole while measuring a selected parameter of the subsurface formation. During the traversal of the borehole, the downhole assembly must be able to withstand extreme shock and severe vibration which are imposed on the measuring device.
The severe environment in which these devices are required to operate presents a major problem when designing the subsurface electronics assembly. The requirement that the electronic components be mounted on a relatively long and slender chassis will leave the assembly susceptible to damage due to extreme shock and severe vibration unless the chassis is securely retained within the housing. Further, the chassis member must be securely retained within the housing by a retaining method which allows simple removal and installation of the chassis within the housing.
Accordingly, the present invention overcomes these difficulties by providing method and apparatus for protecting the subsurface electronics from damage due to shock and vibration while providing easy removal and reinsertion of the electronics assembly within the protective housing.